On the travel surface of a paved road, such defects as a subsidence or deformation, a peeling off on the paved surface, a crushing of a paved surface are generated on the surface from such influencers as degradation over time, ground changes, excessive load, vibration, damages caused by falling objects.
Since such defects can signify serious destruction of a paved road, inhibit stability while traveling, and cause a noise incident to travel, it is imperative to detect early and repair these defects in maintenance management of the road.
The inspection of the travel surface of the paved road is largely grouped into the inspection method by photographing the road surface along the reference axis intersecting the travel direction of the vehicle and the inspection method performed along the reference axis along the travel direction of the vehicle.
Among the above inspection methods, the latter is required to analyze the flatness of the road travel surface.
As the prior arts used in such an inspection for the flatness of the road travel surface, Japanese Patent Application Laid-open No. 2003-315001, Japanese Patent Application No. 2005-315675, and Japanese Patent Application Laid-open No. 2012-173095 are already disclosed, for example.
In Japanese Patent Application Laid-open No. 2003-315001, the shape of the travel surface is inspected based on the displacement of the relative position of a plurality of rollers in contact with the travel surface, following on the road surface.
In Japanese Patent Application No. 2005-315675, the shape of the travel surface is inspected based on the acceleration or speed in the vertical direction of the suspension provided between the main body and the wheel of the vehicle.
These conventional arts include a contact-type device using rollers or wheels in contact with the travel surface, and the contact-style device bumps when the travel surface has a step and fails to inspect the shape of road surface with high-accuracy.
The Japanese Patent Application Laid-open No. 2012-173095 is a contactless conventional technology for inspecting the shape of the travel surface by using the accelerometer and a plurality of lasers.
When the travel surface has a step, even this contactless conventional technology fails to measure the step precisely.
Besides, in the above three kind of the prior arts, the inspection requires the vehicle speed to be maintained so as not to generate acceleration and deceleration exceeding the predetermined range.
Furthermore, in the above prior arts, no information capable of faithfully reproducing the unevenness of the shape of the travel surface can be acquired, no local displacement such as a step can be measured, scattering of aggregate on the surface of paved surface, etc. cannot be measured, and no clogging of spaces on the high-function pavement (a kind of permeable pavement) can be evaluated.
In addition, when the road travel surface is inclined or the vehicle gets on a step, the accompanying change of vehicle posture affects the acceleration in the measurement and causes the precise measurement to be inhibited.
By the way, IRI (traversing profile) measurement index is noted here as an estimation index for a road travel surface.
This IRI represents International roughness index, and is obtained by analyzing traversing profile data with IRI analysis program and calculated on the basis of information obtained from a laser displacement sensor, acceleration detector and speed detector, for example.
This IRI measurement is used for evaluating comfortableness of a traveling vehicle, and the evaluation using such an IRI measurement is regarded as globally common specifications.
At present, this evaluation system is used domestically in an expressway, etc.
However, the conventional IRI measurement requires a stable travel of the vehicle with the speed of 30-40 km/h or more, and thus, in the urban area where vehicles repeatedly stop, depart and perform acceleration and deceleration, and often travel with low speed, appropriate measurement results cannot be obtained due to the influence from the acceleration and deceleration, and any conditions such as measurement speed disperse the measurement accuracy and inhibit the measurement accuracy reference to be set.
Therefore, it is difficult to standardize IRI.
Besides, recently in the field of road travel surface state inspection, a light section method by photographing with the direction intersecting the travel direction as a reference axis is being developed.
Such a light section method is highly appropriate for inspecting the road travel surface state, whereas in the light section method performed by photographing the reference axis along the travel direction, a vehicle inclination state change or influence from acceleration and deceleration accompanied by the travel inhibits high-accuracy photographing, and no technique capable of effectively eliminating this problem has not yet been disclosed.